Field of the Invention
The present invention relates to an axial compressor for a gas turbine or for industrial use, which includes an intake air spray, and an operation method of the axial compressor.
Description of Related Art
In the operation of a gas turbine in the summer season, for example, when the atmospheric temperature is high, the intake air density lowers, thus the gas turbine output reduces. To cope with this output reduction, there is a method of improving the gas turbine output due to the effect of intake air cooling obtained by spraying liquid drops such as water to sucking air of the compressor and thereby increasing the intake air density. Furthermore, when the spray rate of the liquid drops is increased and the liquid drops are introduced into the compressor, due to the effect of intermediate cooling, the compression work is reduced, thus the gas turbine efficiency is improved. Fine liquid drops transferred into the compressor along with the air flow evaporate up to the saturated temperature at the stages as they pass through the rotor blades and the stator vanes, and then the evaporation latent heat reduces the operating fluid temperature.
In a multistage axial compressor, the main flow temperature falls as the liquid drops are vaporized from the upstream side of the compressor, so that the load distribution in the flow direction becomes different from that of the general operation, such that the blade loading reduces on the upstream side of the compressor, while the blade loading increases on the downstream side. Generally, in the partial load operation of a gas turbine, the blade loading on the downstream side of the compressor becomes larger than that on the upstream side, so that when liquid drops are sprayed at the time of partial loading, the blade loading on the downstream side is increased more, thus there is a risk of reducing the blade reliability. Therefore, the spraying of liquid drops is started at the time of stable operation when the gas turbine reaches the rated load.
Further, in the compressor, the clearance between the inner wall surface of the casing and the outer peripheral portion of the rotor blades varies with the thermal expansion difference between the rotor and rotor blades and the casing and if the thermal expansion of the casing is larger than that of the rotor, the tip clearance of the rotor blades is increased and the efficiency of the compressor is reduced extremely. Inversely, if the thermal expansion of the rotor or rotor blades is excessively larger than the thermal expansion of the casing, there is a possibility that the rotor blades and the inner wall surface of the casing will make contact with each other to cause damage to the tips of the rotor blades. In the compressor of a general simple cycle gas turbine, in consideration of the thermal expansion difference, the rotor blade tip clearance is designed so as to be optimum at the time of the rated operation. However, in a compressor in which a large quantity of liquid drops are sprayed for the intake air of the gas turbine to execute intermediate cooling, the liquid drops are sprayed at the time of rated operation, so that the thermal deformation of the casing is utterly different from that of the general simple cycle gas turbine.
Under control of the rotor blade tip clearance of the simple cycle gas turbine, the thermal expansion difference between the casing of the compressor and the rotor and rotor blades maximizes in the high-temperature region at the downstream stage of the compressor, so that as a control structure for the rotor blade tip clearance, there is, for example, one indicated in the patent literature 1. The patent literature 1 discloses a technology of cooling the inner casing of the compressor from the periphery thereof by bleed air bled from the intermediate stage of the compressor, thereby reducing the temperature incline of the compressor in the axial direction so as to control the clearance between the inner wall surface of the casing and the rotor blade tip.